News photos from India on Tuesday showed a large opening in the underbelly of the plane, but apparently it did not extend into the pressurized part of the airplane.
The reports said the missing panel has not been located.
Boeing spokeswoman Lori Gunter said the panel that fell off, known as the mid-underwing-to-body fairing, is located on the belly of the airplane on the right side.
She said the panel is a nonstructural part that aerodynamically contours the surface between the wing and the underbelly and covers the jet's air conditioning packs.
"The event posed no risk to the continued safe operation of the flight," Gunter added. "We're engaged with Air India to provide support needed."
Boeing's description implies that the panel must be removable by airline mechanics to service the air conditioning packs.
That raises the possibility that the panel was improperly replaced after servicing by an Air India mechanic.